数据库：INFORMATION_SCHEMA
表：PROCESSLIST

mysql> desc PROCESSLIST;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| ID      | bigint(4)   | NO   |     | 0       |       |
| USER    | varchar(16) | NO   |     |         |       |
| HOST    | varchar(64) | NO   |     |         |       |
| DB      | varchar(64) | YES  |     | NULL    |       |
| COMMAND | varchar(16) | NO   |     |         |       |
| TIME    | int(7)      | NO   |     | 0       |       |
| STATE   | varchar(64) | YES  |     | NULL    |       |
| INFO    | longtext    | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
8 rows in set (0.00 sec)

select 
　　substring_index(host,":",1) as host, count(1) as cnt 
from (select * from INFORMATION_SCHEMA.PROCESSLIST) a 
group by 
　　substring_index(host,":",1) order by cnt desc;

select db,count(1) as cnt from INFORMATION_SCHEMA.PROCESSLIST group by db order by cnt desc;